Download Weather: Chapter 14

Weather: Chapter 14
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Sec 14.1
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Meteorology
– The study of atmospheres and weather
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Meteorologist
– Someone who studies atmospheres and
weather.
Sec 14.2:Weather Systems
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Weather systems
– Set of temperatures, wind pressures,
moisture conditions for a region that moves
as a unit for a period of days.
– In N. America they are pushed west to east
by mid-latitude westerlies.
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Air Masses
– Large body of air in which the temperature and
moisture content at a specific altitude are fairly
uniform.
– Air mass stays stationary for a period of time
• Can be small 100Km or large 1000Km
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Four main air masses of N. America
–
–
–
–
Maritime polar
Continental polar
Maritime tropical
Continental tropical
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Maritime air masses
– Formed over water
– Are moist, bring rain
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Continental air masses
– Formed over land
– Are dry
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Polar
– Formed at poles
– Are cold
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Tropical
– Formed around equator
– Are warm
North American Air Masses and
the weather they “bring”.
Polar
(cold)
Tropical
(warm)
Maritime
(wet)
Cold/wet
Warm/wet
Continent
al (dry)
Cold/dry
Warm/dry
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Fronts:
– Leading edge of a moving air mass.
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Warm Front:
– Warm air moves into/over a cold air mass
and carries moisture .
– Creates nimbostratus clouds.
Direction of air mass movement is
indicated by the direction of the
“bumps”
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Cold front
– Cold air moves into/under a warm air
mass.
– Creates cumulus clouds, heavy
precipitation.
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Stationary Front
– Boundary between warm air mass and cold
air mass remains still for some time.
– Appears on weather maps as:
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Occluded front
– A cut-off or closed front.
– As a storm grows,one front rotates around
the storm and catches another. This forms
an occluded front, which is the boundary
that separates the new air mass (to the
west) from the older air mass already in
place.
Fronts and Systems:
Regional Weather
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General weather conditions of a region
such as temperature, humidity,
precipitation, and winds
Convection Current

When a temperature difference occurs
in a fluid (water or atmosphere). Hot
fluid rises and cold fluids sink which
create a current or movement in the
fluid
Sec 14.4 Regional Weather
1. Thermals
– The uneven heating of the Earth’s surface
from radiation
– Are created when;
• sun heats land,
• energy absorbed by the land heats the air
• air warms, expands and rises.
Sea Breeze: day time
A warm breeze flowing over the land from the
sea that occurs during the day when land
warms because a convection current is created
when:
 Warm air over land rises
 Sea breeze moves inland replacing the air
 Upper cool air cools and sinks
Land breeze
A cool breeze blowing towards the sea at night
because land cools faster at night and the
waters are warmer
 Warm air over water rises
 Cool air over land sinks
 Land breeze moves out over water to replace
warm air
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Chinook Winds
– Warm dry wind that results from orographic
lifting.
• Wind hits mountain, rises, moisture condenses
with altitude increase
• Condensation releases energy and warms the
air.
• Air that gets to other side of mountain is warm
and dry.
Precipitation
Water which can change form in the
atmosphere.
 Solid or liquid form (depends on ground
and air temperatures).
 Found in cumulus clouds.
 Made via condensation, freezing and
sublimation.

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Dew
– Created when moisture in air contains
condenses on a cool surface near the
ground.
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Frost
– sublimation on a very cold surface.
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Drizzle
– Fine water droplets
– Less than 0.5 mm in diameter.
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Hail
– Forms in troposphere (in thunder clouds)
• Ice pellets move up and down in troposphere.
• Each rise upward passes them through cold
water droplets.
• They grow larger as the freezing water droplets
form more and more ice layers (~ 20 layers).
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Ice pellets/sleet
– Small hard pieces of ice.
– Formed as
• Snow falls through layer of warm air and melts a little.
• It them passes through cold air and re-freezes.
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Rain
– Falling water droplets
– Up to 5mm in diameter.
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Freezing rain
– Rain that hits a very cold surface and freezes
immediately.
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Snow
– Forms when air temp is below 0 degrees
Celsius.
– Water vapour crystallize on dust or other
particles.
– Ice crystals combine and form snow flakes.
– (may turn into sleet/ ice pellets) if it passes
through warm air then cold again.
Meteorological data is collect
using:
Thermometers: temperatures
 Hydrometer/psychrometer: humidity
 Aneroid barometer: barometric/air
pressure
 Anemometer: wind speed, direction
 Rain gauge: level of precipiatation
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